Changes

tmf.ui: make xy chart axis more like the Theia Client

Hide the Y axis line. This removes a harsh graphical element that
does not help trace compass.

[Removed] Remove Y axis gridline from XY charts

Change-Id: I11a52b5f65f115f7bb7684584caff08462135b94
Signed-off-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/c/tracecompass/org.eclipse.tracecompass/+/202066
Tested-by: Trace Compass Bot <tracecompass-bot@eclipse.org>
Tested-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-by: Patrick Tasse <patrick.tasse@gmail.com>